The present invention relates to a method of producing a sewing seam, and more particularly to a method in which predetermined lengths of needle thread are provided at the sewing needle at the end of one sewing step and on the back of the sewing material at the beginning of the next sewing step.
German Patent 27 43 727 C3, which corresponds to U.S. Pat. No. 4,077,342, discloses a device for cutting the needle thread and bobbin thread in an automatic sewing machine. With the known device, on the one hand, short cut-off ends of the bobbin thread and the needle thread remain on the back of the sewn material after the threads are cut; while, on the other hand, sufficiently long initial lengths of bobbin thread and needle thread are provided for the next stitch. In particular, the initial piece of needle thread must be long enough so that, first of all, it does not come out of the eye of the sewing needle when the needle bar is moved to begin formation of the first stitch; and secondly, the end of the initial piece of needle thread is held in the sewing material by friction while the widened loop of needle thread is being moved around the looper until, finally, the formation of the first stitch is completed by knotting the needle thread to the bobbin thread.
The disadvantage of the procedure which has Just been described is that the sufficiently long initial piece of needle thread, which is required for the dependable formation of the first stitch, hangs down from the sewn material at the start of the seam. It must either be subsequently cut off (in the subsequent "cleaning" of the seam), or covered by the next stitch, or one of the next stitches, on the back of the material. When the needle thread is sewn in place in the above-mentioned manner, it forms an unattractive lump of thread which is frequently objectionable.
The subject matter of all prior art material referred to herein is expressly incorporated by reference.